1. Technical Field
The present disclosure relates to illumination, and more particularly to control of a plurality of illumination devices and systems.
2. Description of the Related Art
Luminaires enjoy widespread use in a variety of industrial, commercial, and municipal applications. Such applications can include general or area lighting of workspaces, roadways, parking lots, and the like. Multiple luminaires are typically arranged in patterns and positioned at intervals sufficient to provide a minimum overall level of illumination across the area of interest. For example, luminaires may be spaced at intervals along a driveway in a multilevel parking garage to provide an overall level of illumination that permits safe ingress and egress by pedestrians as well as permits safe operation of motor vehicles within the parking garage. In a similar manner, luminaires may be spaced at intervals throughout a commercial center parking lot to promote safe operation of motor vehicles, permit safe ingress and egress by customers, and foster a sense of safety and well-being for business patrons within the commercial center. Similarly, a number of luminaires may be spaced along a roadway to provide a level of area illumination permitting safe operation of motor vehicles on the roadway and, where applicable, safe passage of pedestrians on sidewalks adjoining the roadway.
To simplify power distribution and control wiring, such luminaires may be organized into groups or similar hierarchical power and control structures. For example, multiple luminaires along a roadway may be grouped together on a common power circuit that is controlled using a single, centralized controller to collectively adjust the luminous output of all of the luminaires in the group. In another instance, multiple luminaires within a parking garage may be controlled using a single photocell mounted on the exterior of the parking garage. Such installations may however compromise operational flexibility for ease of installation and simplicity of operation.
Energy conservation has become of ever-increasing importance. Efficient use of energy can result in a variety of benefits, including financial benefits such as cost savings and environmental benefits such as preservation of natural resources and reduction in “green house” (e.g., CO2) gas emissions.
Residential, commercial, and street lighting which illuminate interior and exterior spaces consume a significant amount of energy. Conventional lighting devices or luminaires exist in a broad range of designs, suitable for various uses. Lighting devices employ a variety of conventional light sources, for example incandescent lamps, fluorescent lamps such as high-intensity discharge (HID) lamps (e.g., mercury vapor lamps, high-pressure sodium lamps, metal halide lamps).
There appear to be at least two primary approaches to reducing energy consumption associated with area lighting systems. One approach employs higher efficiency light sources. The other approach selectively provides light only when needed.
Use of higher efficiency light sources may, for instance, include replacing incandescent lamps with fluorescent lamps or even with solid-state light sources (e.g., light emitting diodes (LEDs), organic LEDs (OLEDs), polymer LEDs (PLEDs)) to increase energy efficiency. In some instances, these higher efficiency light sources may present a number of problems. For example, fluorescent light sources may take a relatively long time after being turned ON to achieve their full rated level of output light or illumination. Such light sources also typically have a high energy consumption during warm-up. Many higher efficiency light sources emit light with a low color rendering index (CRI). For reference, sunlight has a CRI of 100 and represents “ideal light” which contains a continuous spectrum of visible radiation. Low CRI light is less pleasing to the human eye. Surfaces illuminated with low CRI light may not be perceived in their “true” color. Low CRI light makes it more difficult to discern details, often requiring a higher level of output light or illumination to discern details that would otherwise be discernable in high CRI light. Further, higher efficiency light sources may require additional circuitry (e.g., ballasts) and/or thermal management techniques (e.g., passive or active cooling).
Providing area illumination only when needed can be achieved manually by a user of the lighting system, or automatically through the use of one or more control mechanisms. Automatic control mechanisms generally fall into two broad categories, timers and environmental sensors. Timer-based control mechanisms turn light sources ON and OFF based on time. The times are typically user configurable and result in the luminaire turning ON for a period of time and then OFF for the remainder of a 24 hour period. Such timing circuits rely on the user to account for changes in length of daylight which may occur throughout a year by adjusting the ON period of the luminaire commensurate with the change in day length. Very often, timer-based control mechanisms are set once and never updated.
Automatic control devices such as photosensitive transducers (photosensors) and motion or proximity sensors add to the cost of a light fixture, and are frequently mounted in exposed positions where environmental or physical damage is unavoidable or vandalism may occur. In addition, a failure of the automatic control mechanism, for example failure of a photosensor used to turn the light source ON or OFF dependent upon the measured ambient light level, may result in the light source remaining in a continuously ON state in the event the automatic control mechanism fails in a “closed” position, permitting current flow to the light source, or in a continuously OFF state in the event the automatic control mechanism fails in an “open” position, interrupting current flow to the light source. Either failure mode results in an undesirable mode of operation of the light source.
Generally, a photocontrol is a device that switches or controls electrical loads based on ambient light levels. As an example, a photocontrol can be used as a switch that provides electrical power to a luminaire only when detected light levels are below a desired level. Photocontrols used for such luminaires may include photosensors that are electrically and operably coupled to switching devices rated for use at relatively high line voltages (e.g., 90 VAC to 600 VAC) and at relatively high currents (e.g., amperes and higher). For example, a photocontrol for a luminaire may include a photosensor that controls an electro-mechanical relay coupled between a source of electrical power and a control device (e.g., a magnetic or electronic transformer) within the luminaire. The electro-mechanical relay may be configured to be in an electrically continuous state unless a signal from the photosensor is present to supply power to the luminaire. If the photosensor is illuminated with a sufficient amount of light, the photosensor outputs the signal that causes the electro-mechanical relay to switch to an electrically discontinuous state such that no power is supplied to the luminaire.
A typical electro-mechanical relay used with a photocontrol for a luminaire has a relatively short life span. For example, electro-mechanical relays of conventional photocontrols used with luminaires may be rated to have only 5000 contactor closures with standard loads. Arcing caused by high capacitive in-rush currents of electronically ballasted luminaires and inductive “kick back” of magnetically ballasted luminaires can corrode the contactors of the electro-mechanical relays. Additionally, the contactors may include silver or other metal alloys upon which oxides and sulfides may form during normal operation. At line voltage and current, such oxides and sulfides may present a negligible resistance to the passage of current through the contactors. However, at relatively low voltages (e.g., 2V to 24V) and relatively low currents (e.g., microamps) such as those used for digital logic level signaling, the impedance presented by contaminants including oxide and sulfide accumulations can hinder or even prevent the transmission of current through the contactors. Thus, conventional photocontrols for luminaires can have especially short life spans when used in applications where the switching of relatively low voltage and relatively low current signals is required, for example, with luminaires that include solid-state light source drivers, for example, light emitting diode (LED) drivers that receive control signals for LED arrays.
Due to the relatively short life span, photocontrols are a weak link in the reliability chain for illumination systems. Often, service trips to replace a faulty photocontrol may cost significantly more than the photocontrol itself. Previous attempts at circumventing the service of luminaires because of faulty photocontrols have included attempts to design more robust (and more expensive) photocontrols, adding auxiliary ambient light sensors to luminaires that take over control in the event of primary photocontrol failure, and monitoring photocontrols and using a time source such as a real-time clock to control the operation of a luminaire in the event of a photocontrol failure.